Molecular self-assembly is the process of molecules able to associate into more ordered structures. Examples of self-assembling molecules is a class of ultrashort amphiphilic peptides with a distinct sequence motif, which consist of only three to seven amino acids. These peptides can self-assemble to form nanofibrous scaffolds, such as in form of hydrogels, organogels or aerogels, due to their amphiphilic structure which contains a dominant hydrophobic tail and a polar head group. Interestingly, these peptide scaffolds offer a remarkably similar fiber topography to that one found in collagen which is a dominant part of the extracellular matrix. The resemblance to collagen fibers brings a potential benefit in using these peptide scaffolds together with native human cells. Specifically, they can maintain high water content over 99 % weight per volume and are suitable for tissue engineering and regenerative medicine applications. Over the last decade, they have shown promising therapeutic potential in treating several diseases thanks to their high activity, target specificity, low toxicity, and minimal nonspecific and drug-drug interactions. This dissertation describes how to characterize and use ultrashort amphiphilic peptides for tissue engineering and biomedicine. The first chapter offers an overview of already reported self-assembling ultrashort peptides and their applications. As a proof-of-concept, ultrashort peptide scaffolds were used for osteogenic differentiation. Peptide nanoparticles were embedded into 5 peptide hydrogels with the goal to tune the stiffness of the peptide gels. Furthermore, the peptide scaffold was used for the generation of gold and silver nanoparticles after UV irradiation, which allowed the production of nanoparticles in the absence of any additional reducing agent. The mechanism of the generation of these nanoparticles was then investigated. The last chapter describes how tetrameric peptide solutions were utilized for 3D bioprinting applications. Compared to earlier reported self-assembling ultrashort peptide compounds, these tetrapeptides can form hydrogels at an extremely low concentration of 0.1% w/v in a relatively short time under physiological conditions. These promising findings suggest that the peptide solutions are promising bioinks for use in 3D bioprinting.

An alarming increase of antibiotic-resistant bacterial strains has made the demand for novel antibacterial agents, for example, more effective antibiotics, highly crucial. One of the oldest antimicrobial agents is elementary silver which has been used for thousands of years. Even in our days, elementary silver is used for medical purposes, such as for burns, wounds, and microbial infections. We have taken the effectiveness of elementary silver into consideration to generate novel antibacterial and antifouling agents. Our innovative antibacterial agents are hybrid peptide silver nanoparticles (CH-01-AgNPs) that are created de novo and in situ from a silver nitrate solution (AgNO3) in the presence of ultrashort self-assembling peptides compounds. The nucleation of CH-01-AgNPs is initiated by irradiating the peptide solution mixed with the AgNO3 solution using ultraviolet (UV) light at a wavelength of 254 nm, in the absence of any reducing or capping agents. Obviously, the peptide itself serves as the reducing agent. The ultrashort peptides are four amino acids in length with an innate ability to self-assemble into nanofibrous scaffolds. Using these ultrashort peptides CH-01 we were able to create hybrid peptide silver nanoparticles CH-01-AgNPs with a diameter of 4-6 nm. The synthesized CH-01-AgNPs were further characterized using ultraviolet-visible spectroscopy, transmission electron microscopy, dynamic light scattering, and X-ray photoelectron spectroscopy. The antibacterial and antifouling activity of CH-01-AgNPs were then investigated using either gram-negative bacteria, such as antibiotic-resistant Top10 Escherichia coli and Pseudomonas aeruginosa PDO300, or gram-positive bacteria, such as Staphylococcus aureus CECT 976. The hybrid nanoparticles demonstrated very promising antibacterial and antifouling activity with higher antibacterial and antifouling activity as commercial silver nanoparticles. Quantitative Polymerase Chain Reaction (qPCR) results showed upregulation of stress-related genes, e.g. osmB and bdm. Biocompatibility studies of CH-01-AgNPs, using concentrations of 0.06 mM and 0.125 mM, testing for the viability of human dermal fibroblast neonatal (HDFn) cells, showed no significant influence on cell viability. In summary, we consider hybrid peptide silver nanoparticles CH-01-AgNPs as promising biomaterials that can be utilized in various biomedical applications, in particular for wound healing and biofilm inhibition, but also for other applications, such as tissue engineering, drug delivery, regenerative medicine, and biosensing.

The recent upsurge of multidrug resistant bacteria (MDRB) among global communities has become one of the most serious challenges facing health professionals and the human population worldwide. Cationic ultrashort antimicrobial peptides (USAMPs) are a promising group of molecules that meet the required criteria of novel antimicrobial drug development. UP-5, a novel penta-peptide, displayed significant antimicrobial activities against various standard and clinical isolates of MDRB. UP-5 displayed MICs values within the range of (10–15 M) and (55–65 M) against Gram-positive and Gram-negative bacteria, respectively. Furthermore, UP-5 displayed antibiofilm activity with minimum biofilm eradication concentration (MBEC) value as equal to twofold higher than MIC value. At the same inhibitory concentrations, UP-5 exhibited very low or negligible toxicity toward human erythrocytes and mammalian cells. Combining UP-5 with conventional antibiotics led to a synergistic or additive mode of action that resulted in the reduction of the MIC values for some of the antibiotics by 99.7% along a significant drop in MIC values of the peptide. The stability profile of UP-5 was evaluated in full mouse plasma and serum with results indicating a more stable pattern in plasma. The present study indicates that USAMPs are promising antimicrobial agents that can avoid the negative characteristics of conventional antimicrobial peptides. Additionally, USAMPs exhibit good to moderate activity against MDRB, negligible toxicity, and synergistic outcomes in combination with conventional antimicrobial agents.